1. Field of the Invention
The present invention relates to a foamable silicone rubber composition, and more particularly to a foamable silicone rubber composition which have a long pot life, and can be foamed and cured by heating to form a foamed cured product in the form of a sponge having uniform cells.
2. Description of the Prior Art
The foamable silicone rubber compositions capable of forming foamed cured products in the form of a sponge include two types of compositions, that is, compositions which inherently do not have any foamable mechanism per se but have been given foamability by being added with a foaming agent, and silicone rubber compositions which inherently have a cure mechanism accompanied by foamability (see, e.g., Japanese Patent Publication (kokoku) No. 45-12675).
Since the compositions having a cure mechanism accompanied by foamability generally have a short pot life, as an agent for retarding a curing catalyst (typically, a platinum catalyst) is added a polymethylvinyl cyclic compound (Japanese Patent Publication (kokoku) No. 52-42826), or acetylene alcohols (Japanese Patent Publication Nos. 53-5342, 53-24454, 53-48226, 3-26216, etc.) in a small amount to extend the pot life.
The foamable compositions to which a curing catalyst-retarding agent is added, however, have a problem that their pot life is only 20 minutes at longest from the time a composition is prepared by mixing the components at room temperature. Increase in the amount of the curing catalyst-retarding agent for extending the pot life, will result in the cells which are irregular and too large. Therefore, a foamable silicone rubber composition is required which has a longer pot life and is capable of producing a foamed cured product in the form of a sponge having uniform cells.